1. Field of the Invention
The present invention relates to an atomic layer deposition (ALD) method using an organometallic complex with a xcex2-diketone ligand and, more particularly, to an improved ALD method in which chemical species with xcex2-diketone ligands are deposited into atomic layers using activated oxygen radicals using plasma as an energy source.
2. Description of the Related Art
Metal oxide thin films, which are used as high-dielectric thin films, ferroelectric thin films, and electrodes, are generally formed by a sputtering, sol-gel, chemical vapor deposition (CVD), or atomic layer deposition (ALD) method.
In the ALD method, a volatile organometallic compound as a precursor is chemically adsorbed onto a substrate and oxidized to form a desired metal oxide thin film. The ALD method has recently gained great interest because thin film formation by chemical adsorption improves large-area surface uniformity and step coverage with easy control of the metal composition.
To form a metal oxide thin film by the ALD method described above, there is a need for a precursor that is capable of easy chemical adsorption onto a target substrate, having excellent thermal and chemical stability and vaporization characteristics, and a great difference between its vaporization and decomposition temperatures. It is also necessary to create oxidation conditions for rapid oxidation of the chemically adsorbed precursor. In addition, an oxidizing agent such as oxygen and water is required to achieve a high oxidation rate.
Compounds with alkyl or aromatic ligands that are highly decomposable in an oxidation atmosphere have been widely used as the precursor.
For a metal compound having molecular bonds with a low coordination number, alkyl or aromatic ligands bonded to metal atoms by comparatively weak bond strength are enough to ensure high volatility at low temperatures. In addition, because the bonds between the metal atoms and the ligands are easily broken, such a metal compound is very suitable for use as an ALD precursor with high oxidation rate.
When metal atoms, such as barium (Ba) and strontium (Sr), having large bonding volume and large coordination numbers, are coordinated with alkyl or aromatic ligands, a large-weight molecule is formed through bonding of a unit molecule consisting of the metal atom and ligands such as alkyl or aromatic ligands, with reduced volatility. When such a compound having alkyl or aromatic ligands is used as a precursor, high-temperature heating is necessary to increase the vapor pressure of the precursor. However, weak bonds between the metal and ligands are dissociated during the heating process so that use of the precursor is limited. To solve this problem, xcex2-diketone, such as tetramethylheptanedionate (tmhd), having a large volume, has been suggested as a ligand coordinated to a metal atom to prevent bonding of the unit molecule.
However, use of a compound having xcex2-diketone ligands for thermal ALD using oxygen has been limited due to low oxidation rates. For this reason, a precursor with alkyl or aromatic ligands that have poor volatility but is easily oxidized has been mostly used for the ALD. In other words, increasing volatility of the precursor for use in ALD has been unchallenged at the cost of increasing its oxidation rate.
A feature of the present invention is to provide an atomic layer deposition (ALD) method with a high oxidation rate using a highly volatile compound with a xcex2-diketone ligand strongly bonded to metal as a precursor.
According to a preferred embodiment of the present invention, there is provided an atomic layer deposition (ALD) method comprising chemically adsorbing an organometallic complex with a xcex2-diketone ligand onto a substrate and oxidizing the chemically adsorbed organometallic complex using activated oxygen radicals in order to deposit an atomic metal oxide layer on the substrate.
The activated oxygen radicals are generated by reacting plasma as an energy source with at least one oxygen-containing gas selected from the group consisting of oxygen, ozone, nitrogen monoxide, and water vapor. Additionally, the oxygen containing gas may be irradiated with ultraviolet (UV) light during reaction with the plasma to generate the activated oxygen radicals.
The organometallic complex with a xcex2-diketone ligand is expressed by formula (1) below: 
where M is a metal ion with a valence number of 1 to 6; X is O, NH, or S; Y is O, N, or S; and R1, R2, and R3 are independently a hydrogen atom, a linear or branched unsubstituted alkyl group having 2 to 10 carbon atoms, a linear or branched alkoxy group-substituted alkyl group having 2 to 10 carbon atoms, a linear or branched alkoxyalkyleneoxy group-substituted alkyl group having 2 to 10 carbon atoms, or an alkylamine group having 2 to 10 carbon atoms; I is 1 or 2; L is an anionic ligand coordinated to metal M; m is an integer from 0 to 5; A is a neutral ligand; and n is an integer from 0 to 4.
Preferably, in formula (1) above, L is an alkoxy group having 1 to 10 carbon atoms, an alkyl group having 1 to 5 carbon atoms or an alkylamine or alkylsulfide group having 1 to 10 carbon atoms, and A is ether or amine with a coordination number by which all coordination locations of the cationic metal are saturated.
These and other features and aspects of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.